Communication by means of electromagnetic waves has progressed dramatically since Gulielmo Marconi's demonstration in 1897 of the ability to provide communication with ships sailing the English Channel. From this demonstration sprang many applications including radio, television, and personal communication. Indeed, it is expected that developments in communications will continue.
In developing a communications system, it is generally advantageous for a communications link to utilize the strongest signal feasible for improving signal quality and for providing sufficient coverage or range. With regard to signal quality, a stronger signal yields a higher signal-to-noise ratio. Also, a stronger signal propagates a longer distance. Importantly, signal power must be constrained within limits. For example, in most situations, limits are imposed by governmental agencies such as the Federal Communications Commission (FCC). Indeed, this is important so as to prevent one or more powerful signals from interfering with the communications of other signals in the same frequency range. Other restrictions may be imposed by standards committees or may be self-imposed by a system in order to minimize interference where several signals are expected to simultaneously exist.
An important consideration in designing a communication system is its performance over a wide temperature range because it has been observed that the characteristics of a communication system change over temperature in such a way that its transmission power is affected. For example, while maintaining all other conditions constant, a communication system can transmit at a lower power levels at elevated temperatures and it can transmit at a higher power levels at very cold temperatures, and vice-versa. Whatever the characteristics of a communications system may be, it is nonetheless desirable to closely monitor and control the transmission power. For example, it is desirable to control the maximum allowed power level. It is therefore important to know a communication systems transmission power level at any temperature of operation. Conventional approaches have been placing a power detector within the communication system along with a temperature sensor so as to develop a calibration table. In conventional calibration methods, the entire communication system used to be exercised at various temperatures while noting the output of the detector circuit. When placed in service, the communication system would then retrieve calibration data at a measured temperature so as to accurately measure the system's transmission power. Such conventional calibration methods, however, necessarily required that the entire system, or at least a large part of the system, be placed in a temperature chamber. Because of the sizes and masses involved, the calibration system is slow. Moreover, because an entire system is calibrated, any changes in components, such as upon a failure, required re-calibration.